The present invention relates to dynamoelectric machines and more particularly to a one-piece end bell and brush holder for a dynamoelectric machine.
The brushes of a motor or generator that has a drum-like commutator are generally oriented in a radial direction about the circumference of the commutator and are biased inwardly against the commutator. Brushes are thus conventionally received within a brush holder for supporting and guiding the motor brushes to ensure their proper orientation and location. A separate end bell encloses the commutator end of the motor or generator and secures the brush holder in its proper position.
Various arrangements have been developed for mounting brushes. One such arrangement is shown in Spors, U.S. Pat. No. 3,745,393, which is assigned to the assignee of the present invention. The Spors patent discloses a two-piece brush holder that comprises a molded carrier having a plurality of brush receiving recesses formed therein and a stamped washer-like member to insulate the brushes from the motor housing. A separate end bell encloses the commutator end of the motor, and secures the brush holder in its proper position. Such an assembly, however, entails relatively high costs of fabrication and assembly due to the number of individual parts thereof. It is thus desirable to provide a unitary brush holder comprised of simple and inexpensive parts which can be economically manufactured and assembled.
Various unitary brush holders have also been developed. One such unitary structure is shown in Wan, U.S. Pat. No. 4,112,321, which discloses a molded plastic brush holder. The brush holder includes brush housings formed therein that provide channelways for supporting and guiding motor brushes. Each housing includes sidewalls having projecting ribs that engage with mating grooves formed in each brush, and a finger that extends from a rear wall along one of the open ends of the channel. The finger and ribs of each housing serve to prevent a biasing spring from falling through the open ends of the brush channel. Although the brush holder of Wan is molded in one piece, it would still be necessary to utilize a separate end bell to enclose this type of brush holder in a motor housing. There is therefore little, if any, cost advantage in utilizing such a brush holder.
Various problems in addition to cost are also associated with brush holder assemblies. One such problem involves the heat generated as a result of friction between the brushes and the rotating commutator. A brush holder assembly must provide for the dissipation of such heat to decrease brush wear and increase motor life. One solution is to construct the brush holders from a material which is a good conductor of heat. Another solution includes exposing the surface area of the brushes to the atmosphere. For example, in the aforesaid Wan patent two faces and the back side of each brush are exposed to the atmosphere. However, the two remaining faces of each brush are still substantially confined within and in contact with the side walls of the brush holding housings. It is, therefore, desirable to not only construct a brush holder from a material which is a good conductor of heat, but also to expose as much as possible of the surface area of each brush to the atmosphere to provide adequate heat dissipation.
Another problem associated with friction between the brushes and the rotating commutator is that of brush wear. Brush wear causes fine dust particles to develop within the assembly. Such dust may adhere to the brush terminals resulting in corrosion and an electrical connection of reduced efficiency.
Provision should also be made for ease of assembly. Brush lead wires or shunt wires connecting the brushes and terminals need to be located in such a position so as to avoid interference with the commutator when the brushes are assembled about the commutator. For example, the aforesaid Wan patent utilizes U-shaped members for retaining conductor wires, but does not provide for retaining the lead or shunt wires.
It is thus desirable to combine a brush holder with an end bell into a one-piece structure which would substantially reduce the problems relating to cost, heat, wear and assembly presented by prior brush holder assemblies.